Method for manufacturing dental implant and dental implant

ABSTRACT

A dental implant capable of reliably preventing elution of metal when the dental implant is applied within an oral cavity and capable of reliably preventing the occurrence of mismatching (bumpy occlusion or the like) when the dental implant is fixed in place. The dental implant includes an abutment comprising a titanium member composed of a sintered body made from titanium or titanium alloy, and a ceramic member composed of a sintered body made from oxide-based ceramic. One of the titanium member and the ceramic member has a recess and the other of the titanium member and the ceramic member has a protrusion inserted into the recess. The shape of the protrusion conforms to the recess.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims a priority to Japanese Patent Application No.2007-196497 filed on Jul. 27, 2007 which is hereby expresslyincorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to a method for manufacturing a dentalimplant and a dental implant manufactured by the method.

2. Related Art

An implant (dental implant) has been extensively used to restore thefunction of a tooth lost by various causes. In general, the dentalimplant includes a fixture anchored to a jawbone and an abutmentthreadedly coupled to the fixture.

A crown restoration is capped on the dental implant (the abutmentthreadedly coupled to the fixture) and fixed thereto with dental cement,thereby bringing the dental implant into a shape corresponding to thatof an original tooth.

Conventionally, from the standpoint of compatibility to a living body,strength and so forth, titanium or titanium alloy has been generallyused as a constituent material of the implant (see, e.g.,JP-A-2000-24004, page 3, right column, lines 40 to 42).

Ceramic is generally used as a constituent material of the crownrestoration to lessen the difference in appearance between the crownrestoration and the tooth of a living body.

A metal portion (metal layer) made of gold alloy or the like is arrangedon the inner surface (the implant-side surface) of the crown restorationin an effort to improve occlusion or to reliably prevent occurrence ofcracks in the crown restoration.

In other words, a laminated body including a metal portion (metal layer)made of metal and a layer made of ceramic is widely used as the crownrestoration.

If the crown restoration has the metal portion as set forth above,however, a galvanic cell is formed between the metal portion and thetitanium-made implant. This may possibly cause metal to be eluted intothe living body, thereby adversely affecting the living body.

With a view to avoid such a problem, it would be conceivable that themetal portion of the crown restoration is fixed to the implant with arelatively large quantity of dental cement so that they should not makecontact with each other.

In this case, it becomes difficult to adjust the height and angle of thecrown restoration to be fixed to the implant as designed at the outset.It is also difficult to obtain sufficiently high bonding strength.

In order to prevent contact between the titanium or titanium alloy ofwhich the implant is made and the metal portion of the crownrestoration, it would also be conceivable that the titanium or titaniumalloy is coated with insulating ceramic.

Ceramic is usually inferior in its bondability with titanium or titaniumalloy, although it exhibits superior bondability with gold alloy. Thismakes it difficult to sufficiently increase the bonding strength betweenthe portion made of titanium or titanium alloy and the portion made ofceramic.

As a result, mismatching (bumpy occlusion or the like) of the implant isapt to occur, consequently deteriorating the feeling of use of theimplant.

SUMMARY

It is an object of the present invention to provide a dental implantcapable of reliably preventing elution of metal when the dental implantis applied within an oral cavity and capable of reliably preventingoccurrence of mismatching (bumpy occlusion or the like) when the dentalimplant is fixed in place, and a method for manufacturing the dentalimplant.

With this object in mind, one aspect of the present invention isdirected to a method for manufacturing a dental implant including anabutment.

The abutment is manufactured through the steps comprising a titaniummolded body production step for molding a titanium molded bodycomposition containing powder composed of titanium or titanium alloy anda binder to obtain a titanium molded body, a ceramic molded bodyproduction step for molding a ceramic molded body composition containingpowder composed of oxide-based ceramic and a binder to obtain a ceramicmolded body, an assembling step for assembling the titanium molded bodyand the ceramic molded body together to obtain an assembled body, adegreasing step for degreasing the assembled body so that the bindercontained in the titanium molded body and the binder contained in theceramic molded body are removed therefrom to transform the titaniummolded body into a titanium degreased body and to transform the ceramicmolded body into a ceramic degreased body, and a sintering step forsintering the assembled body thus degreased to transform the titaniumdegreased body into a titanium member as a sintered body and totransform the ceramic degreased body into a ceramic member as a sinteredbody so that the titanium member and the ceramic member are firmly fixedand joined together.

The method of the present invention is capable of reliably preventingelution of metal when the dental implant is applied within an oralcavity and capable of reliably preventing occurrence of mismatching whenthe dental implant is fixed in place.

In the method of the present invention, it is preferred that one of thetitanium and ceramic molded bodies has a recess, and the other moldedbody has a protrusion inserted into the recess, wherein a contentpercentage of the binder contained in the molded body having the recessis greater than that of the molded body having the protrusion.

This makes it possible to greatly increase adhesion and fixing strengthbetween the titanium member and the ceramic member and to effectivelyprevent occurrence of mismatching when the dental implant is fixed inplace.

In the method of the present invention, it is preferred that the contentpercentage of the binder contained in the molded body having theprotrusion is in the range of 3 to 35 wt %.

This makes it possible to obtain a molded body having a protrusion withincreased moldability and to greatly increase adhesion and fixingstrength between the titanium member and the ceramic member in thedental implant finally obtained.

Furthermore, it is possible to effectively prevent the molded bodyhaving the protrusion from being inadvertently deformed in thedegreasing process, which in turn makes it possible to greatly increasedimensional accuracy of the dental implant finally obtained.

In the method of the present invention, it is preferred that the contentpercentage of the binder contained in the molded body having the recessis in the range of 6 to 40 wt %.

This makes it possible to effectively prevent the molded body having therecess from being inadvertently deformed in the degreasing process andto greatly increase adhesion and fixing strength between the titaniummember and the ceramic member in the dental implant finally obtained.

Furthermore, it is possible to obtain a molded body having a recess withincreased moldability.

In the method of the present invention, it is preferred that in the casewhere the content percentage of the binder contained in the molded bodyhaving the recess is defined by C_(A) (wt %) and the content percentageof the binder contained in the molded body having the protrusion isdefined by C_(B) (wt %), C_(A) and C_(B) satisfy a relation of3≦C_(A)−C_(B)≦15.

This makes it possible to greatly increase adhesion and fixing strengthbetween the titanium member and the ceramic member in the dental implantfinally obtained and to effectively prevent the molded body having theprotrusion and the molded body having the recess from beinginadvertently deformed in the degreasing process.

As a result, it is possible to greatly enhance mechanical stability anddimensional accuracy of the dental implant finally obtained.

In the method of the present invention, it is preferred that the recessof the molded body has a size lager than that of the protrusion of themolded body, wherein in the assembling step, the assembled body isassembled by inserting the protrusion of the molded body into the recessof the molded body so that a clearance is existed therebetween, andwherein in the degreasing and sintering steps, when the assembled bodyis degreased and sintered, the molded body having the recess contractsgreater than the molded body having the protrusion so that the clearanceis eliminated, thereby bringing a protrusion of the member into closecontact with and fitting to a recess of the member.

This makes it possible to greatly increase adhesion and fixing strengthbetween the titanium member and the ceramic member and to effectivelyprevent occurrence of mismatching when the dental implant is fixed inplace.

In the method of the present invention, it is preferred that theprotrusion of the molded body has a portion whose cross-sectional areais increased toward a dead-end portion of the recess of the molded bodyin a state that the protrusion of the molded body is inserted into therecess of the molded body.

This makes it possible to greatly increase adhesion and fixing strengthbetween the titanium member and the ceramic member and to effectivelyprevent occurrence of mismatching when the dental implant is fixed inplace.

In the method of the present invention, it is preferred that theprotrusion of the molded body has a portion whose cross-sectional areais continuously increased toward a dead-end portion of the recess of themolded body in a state that the protrusion of the molded body isinserted into the recess of the molded body.

This makes it possible to greatly increase adhesion and fixing strengthbetween the titanium member and the ceramic member and to effectivelyprevent occurrence of mismatching when the dental implant is fixed inplace.

In the method of the present invention, it is preferred that theprotrusion of the molded body has a portion whose cross-sectional shapeis non-circular.

This makes it possible to reliably prevent the titanium member and theceramic member from making relative rotational movement and toeffectively prevent occurrence of mismatching when the dental implant isfixed in place.

In the method of the present invention, it is preferred that the ceramicmember is composed of zirconia as a major component thereof.

Among various kinds of oxide-based ceramics, zirconia is particularlysuperior in living body affinity and strength. If the ceramic member iscomposed of zirconia as a major component thereof, it becomes possibleto remarkably improve safety of the dental implant and also to morereliably prevent occurrence of problems such as gum recession afterapplication of the dental implant. It is also possible to greatlyenhance durability of the dental implant.

Further, among various kinds of oxide-based ceramics, zirconia exhibitsvery low adhesion with titanium or titanium alloy. In a method using anadhesive agent or the like, therefore, adhesion and bonding strengthbetween a member made of titanium or titanium alloy and a member made ofzirconia becomes very low.

However, in the present invention, since the titanium member and theceramic member are firmly fixed and joined together through a sinteringprocess, it is possible to sufficiently increase adhesion and fixingstrength between the titanium member and the ceramic member withoutusing any adhesive.

In other words, effects provided by the present invention become moreconspicuous if the ceramic member is composed of zirconia as a majorcomponent thereof.

In the method of the present invention, it is preferred that the dentalimplant further includes a fixture to be coupled to the abutment andanchored to a jawbone, the fixture made of titanium or titanium alloy.

This makes it possible to greatly increase fixing strength of the dentalimplant to a living body (a jawbone) when the dental implant is appliedto the living body. It is also possible to greatly increase adhesionbetween the fixture and the abutment when the dental implant is appliedto the living body.

In the method of the present invention, it is preferred that the ceramicmember has a contact surface with which a metal having a compositiondifferent from that of a constituent material of the titanium membermakes contact.

This makes it possible to reliably prevent elution of metal when thedental implant is applied within an oral cavity.

Another aspect of the present invention is directed to a dental implantincluding an abutment. The dental implant comprises a titanium membercomposed of a sintered body made from titanium or titanium alloy, and aceramic member composed of a sintered body made from oxide-basedceramic, wherein the titanium member and the ceramic member are firmlyfixed and joined together through a sintering process.

The dental implant of the present invention is capable of reliablypreventing elution of metal when the dental implant is applied within anoral cavity and capable of reliably preventing occurrence of mismatchingwhen the dental implant is fixed in place.

In the dental implant of the present invention, it is preferred that oneof the titanium member and the ceramic member has a recess and the otherof the titanium member and the ceramic member has a protrusion insertedinto the recess.

This makes it possible to greatly increase adhesion and fixing strengthbetween the titanium member and the ceramic member and to effectivelyprevent occurrence of mismatching when the dental implant is fixed inplace.

In the dental implant of the present invention, it is preferred that theprotrusion of the member is in close contact with and fitted to therecess of the member.

This makes it possible to greatly increase adhesion and fixing strengthbetween the titanium member and the ceramic member and to effectivelyprevent occurrence of mismatching when the dental implant is fixed inplace.

In the dental implant of the present invention, it is preferred that theprotrusion of the member has a portion whose cross-sectional area isincreased toward a dead-end portion of the recess of the member.

This makes it possible to greatly increase adhesion and fixing strengthbetween the titanium member and the ceramic member and to effectivelyprevent occurrence of mismatching when the dental implant is fixed inplace.

In the dental implant of the present invention, it is preferred that theceramic member has a contact surface with which a metal member having acomposition different from that of a constituent material of thetitanium member makes contact.

This makes it possible to reliably prevent elution of metal when thedental implant is applied within an oral cavity.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description ofpreferred embodiments given in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front view showing one preferred embodiment of a dentalimplant in accordance with the present invention, in which a fixture andan abutment are threadedly coupled.

FIG. 1B is a front view showing the preferred embodiment of the dentalimplant in which the fixture and the abutment are not threadedlycoupled.

FIG. 1C is a vertical section view showing the preferred embodiment ofthe dental implant in which the fixture and the abutment are notthreadedly coupled.

FIGS. 2A to 2C are views for explaining an operation method using thedental implant.

FIGS. 3A to 3F are process views illustrating one preferred embodimentof a dental implant manufacturing method in accordance with the presentinvention.

FIG. 4A is a vertical section view showing a boundary portion between atitanium molded body and a ceramic molded body which are kept in anassembled state.

FIG. 4B is a vertical section view showing a boundary portion between atitanium member and a ceramic member after a sintering step has beenperformed.

FIG. 5 is a vertical section view showing an abutment manufactured inComparative Example 3.

FIG. 6 is a view schematically illustrating a configuration of a jigused in measuring fixing strength and also explaining a method ofmeasuring the fixing strength.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

FIG. 1A is a front view showing one preferred embodiment of a dentalimplant in accordance with the present invention, in which a fixture andan abutment are threadedly coupled. FIG. 1B is a front view showing thepreferred embodiment of the dental implant in which the fixture and theabutment are not threadedly coupled. FIG. 1C is a vertical section viewshowing the preferred embodiment of the dental implant in which thefixture and the abutment are not threadedly coupled.

FIGS. 2A to 2C are views for explaining an operation method using thedental implant. FIGS. 3A to 3F are process views illustrating onepreferred embodiment of a dental implant manufacturing method inaccordance with the present invention.

FIG. 4A is a vertical section view showing a boundary portion between atitanium molded body and a ceramic molded body which are kept in anassembled state. FIG. 4B is a vertical section view showing a boundaryportion between a titanium member and a ceramic member after a sinteringstep has been performed.

The drawings referred to in this specification show parts of componentsin an exaggerated state and does not accurately reflect the actualdimension thereof.

Dental Implant

First, description will be made on a dental implant in accordance withthe present invention.

A dental implant 10 includes a fixture 1 anchored to a jawbone and anabutment 2 threadedly coupled to the fixture 1.

(1) Fixture

The fixture 1 is a member that will be anchored to the jawbone in anoperation using the dental implant 10. The fixture 1 is formed into abottom-closed tubular shape. A male thread portion 11 is provided on anouter circumferential surface of the fixture 1. This makes it possibleto threadedly anchor the fixture 1 to the jawbone in which a thread isformed by cutting or other methods.

A cutout portion 111 having a specified length is formed in a part ofthe male thread portion 11 to extend in an axial direction of thefixture 1. No spiral groove is formed in the cutout portion 111. Thismakes it possible to threadedly anchor the fixture 1 to the jawbone inan easy and reliable manner during a course of conducting an operation.

After the operation comes to an end, osteogenesis is progressed byosteoblastic cells in a region of a living body corresponding to thecutout portion 111. Therefore, it is possible to effectively prevent thethread coupling from being loosened.

The fixture 1 has a tubular portion 12 into which the abutment 2 isinserted as mentioned below. Formed on an inner circumferential surfaceof the fixture 1 is a female thread portion 13 that can make threadcoupling with a male thread portion 211 of the abutment 2 (a titaniummember 21).

The fixture 1 may be made of any material. From the standpoint of livingbody compatibility, strength and so forth, it is preferred that thefixture 1 is made of titanium or titanium alloy.

(2) Abutment

The abutment 2 is a member that will be fixed to the fixture 1 in theoperation using the dental implant 10. Further, the abutment 2 is cappedby a crown restoration 3 which is used for a purpose of improvingaesthetic appearance and assuring enhanced occlusion.

The abutment 2 includes a titanium member 21 made of titanium ortitanium alloy and a ceramic member 22 made of oxide-based ceramic.

(2.1) Titanium Member

The titanium member 21 is one of constituent members of the abutment 2that will be threadedly coupled to the female thread portion 13 of thefixture 1 as mentioned above. The titanium member 21 has a male threadportion 211 threadedly coupled to the female thread portion 13 of thefixture 1.

The titanium member 21 is made of titanium or titanium alloy. It ispreferred that the titanium member 21 is made of a material having thesame composition as that of a constituent material of the fixture 1.This makes it possible to greatly improve adhesion between the fixture 1and the abutment 2.

Furthermore, this makes it possible to reliably prevent occurrence ofproblems such as elution of metal within an oral cavity due to agalvanic cell formed by an electric potential difference between theconstituent material of the fixture 1 and the constituent material ofthe abutment 2.

In the illustrated configuration, the titanium member 21 has aprotrusion 212 to which a recess 222 formed in the ceramic member 22 isto be fitted as mentioned below. The protrusion 212 is of a shapecomplementary to the recess 222 of the ceramic member 22.

The titanium member 21 is firmly fixed and joined to the ceramic member22 through a joint (engagement) between the protrusion 212 and therecess 222. For this reason, the titanium member 21 and the ceramicmember 22 exhibit extremely superior adhesion between them.

The protrusion 212 has a cross-sectional area increasing portion 213whose cross-sectional area is increased from a base end toward a distalend of the protrusion 212, that is, toward a dead-end portion of therecess 222 of the ceramic member 22.

Provision of the cross-sectional area increasing portion 213 makes itpossible to greatly enhance adhesion and fixing strength (jointstrength) between the titanium member 21 and the ceramic member 22. Itis also possible to more effectively prevent any mismatching (bumpyocclusion or the like) when the dental implant 10 is fixed in place.

Although the cross-sectional area increasing portion 213 may be formedin such a manner that the cross-sectional area of the protrusion 212 isincreased either continuously or non-continuously toward the distal endthereof, it is preferred that the cross-sectional area is increasedcontinuously as shown in the drawings.

This makes it possible to greatly enhance adhesion and fixing strengthbetween the titanium member 21 and the ceramic member 22. It is alsopossible to more effectively prevent any mismatching when the dentalimplant 10 is fixed in place.

An angle θ between a surface (a circumferential surface) of thecross-sectional area increasing portion 213 and a heightwise axis of theprotrusion 212 is not particularly limited to a specific value, but ispreferably in the range of 0.3 to 50, and more preferably in the rangeof 1 to 40.

By setting the angle θ within the above ranges, the ceramic member 22 isprevented from becoming extremely thin in a region around the recess 222of the ceramic member 22. As a result, an effect provided by thecross-sectional area increasing portion 213 grows conspicuous.

In other words, it is possible to greatly enhance adhesion and fixingstrength between the titanium member 21 and the ceramic member 22 whilekeeping strength of the ceramic member 22 sufficiently high. As aconsequence, it is possible to keep durability of the dental implant 10sufficiently high and also to more effectively prevent any mismatchingwhen the dental implant 10 is fixed in place.

In contrast, if the angle θ is smaller than the lower limit value notedabove, there is a possibility that the effect provided by thecross-sectional area increasing portion 213 may not be sufficientlyattained.

On the other hand, if the angle θ exceeds the upper limit value notedabove, there is a possibility that the ceramic member 22 may have aregion with no sufficiently great thickness (a thin region) around therecess 222 to which the protrusion 212 of the titanium member 21 isfitted. This may reduce strength and durability of the dental implant10.

In the illustrated configuration, the cross-sectional area increasingportion 213 is formed over a full heightwise length of the protrusion212. This makes it possible to greatly enhance adhesion and fixingstrength between the titanium member 21 and the ceramic member 22. It isalso possible to more effectively prevent any mismatching when thedental implant 10 is fixed in place.

Furthermore, it is preferred that the protrusion 212 has a portion whosecross-sectional shape is non-circular. This makes it possible to morereliably prevent the titanium member 21 and the ceramic member 22 frommaking relative rotational movement. It is also possible to moreeffectively prevent any mismatching when the dental implant 10 is fixedin place.

In this regard, examples of the non-circular shape include a generallypolygonal shape such as a triangular shape, a rectangular shape, ahexagonal shape or the like, a partially cut-away circular shape, anelliptical shape and so forth.

A height of the protrusion 212 is not particularly limited to a specificvalue, but is preferably in the range of 2 to 5 mm, and more preferablyin the range of 3 to 4 mm. This makes it possible to greatly increasestrength and durability of the abutment 2.

(2.2) Ceramic Member

The ceramic member 22 is a member capped by a crown restoration 3 asmentioned below. In the illustrated configuration, the ceramic member 22has a recess 222 fitted to the titanium member 21 as mentioned above.

The recess 222 is of a shape complementary to the protrusion 212 of thetitanium member 21, thereby keeping adhesion between the titanium member21 and the ceramic member 22 extremely high.

The ceramic member 22 has a metal bonding surface (a contact surface)224 that makes contact with a metal portion 32 of the crown restoration3 when the dental implant 10 is capped by the crown restoration 3 asmentioned below. As set forth above, the ceramic member 22 is made ofoxide-based ceramic.

Among various kinds of materials (especially, various kinds of ceramicmaterials), the oxide-based ceramic is particularly superior in livingbody compatibility and extremely low in living body hazard. Furthermore,the oxide-based ceramic seldom gathers contaminants and exhibitsincreased hardness and strength.

Examples of the oxide-based ceramic of which the ceramic member 22 ismade include zirconia (zirconium oxide), silicon oxide (silica),aluminum oxide (alumina), calcium oxide, sodium oxide, potassium oxide,boron oxide, zinc oxide, magnesium oxide (magnesia), lithium oxide, tinoxide, indium oxide and titanium oxide, one or more of which may be usedindependently or in combination.

Among them, it is preferred that the ceramic member 22 is composed ofzirconia as a major component thereof. Among various kinds ofoxide-based ceramics, zirconia is particularly superior in living bodyaffinity and strength.

If the ceramic member 22 is composed of zirconia as a major componentthereof, it becomes possible to remarkably improve safety of the dentalimplant 10 and also to more reliably prevent occurrence of problems suchas gum recession and the like after application of the dental implant10. It is also possible to greatly enhance durability of the dentalimplant 10.

Further, among various kinds of oxide-based ceramics, zirconia exhibitsvery low adhesion with titanium or titanium alloy. In a method using anadhesive agent or the like, therefore, adhesion and bonding strengthbetween a member made of titanium or titanium alloy and a membercomposed of zirconia becomes very low.

However, in the present invention, since the titanium member and theceramic member are firmly fixed and joined together through a sinteringprocess, it is possible to sufficiently increase adhesion and fixingstrength between the titanium member and the ceramic member withoutusing any adhesive.

In other words, effects provided by the present invention become moreconspicuous if the ceramic member is composed of zirconia as a majorcomponent thereof.

In this regard, it is to be noted that the term “as a major componentthereof” used herein means that a particular component of a materialconstituting a subject member or composition has the greatest content.

A content of the component is not particularly limited to a specificvalue, but is preferably 50 wt % or more, more preferably 55 wt % ormore, and even more preferably 60 wt % or more of the materialconstituting the subject member or composition.

Operation Method Using Dental Implant

Next, an operation method using the dental implant 10 will be describedwith reference to FIGS. 2A to 2C.

Embedding Fixture

After putting a patient under anesthesia, the fixture 1 is threadedlyanchored to a jawbone 50 in which a thread is cut in advance (see FIG.2A). Then, the fixture 1 is covered with a gum 60 if necessary.

Threadedly Coupling Abutment

If osteogenesis is adequately progressed by osteoblastic cells andosteointegration between the fixture 1 and the jawbone 50 is progressedsufficiently after the lapse of a specified time period (usually about 3to 6 months) from the fixture embedding time, the abutment 2 isthreadedly coupled to the fixture 1 anchored to the jawbone 50 (see FIG.2B).

In the case where the fixture 1 is covered with the gum 60, the fixture1 is exposed as appropriate by incising the gum 60 prior to threadedlycoupling the abutment 2.

Capping Crown Restoration

Next, the crown restoration 3 molded by modeling is fixed to the ceramicmember 22 of the abutment 2 (see FIG. 2C) The crown restoration 3includes a ceramic portion 31 made of ceramic and visually recognizedfrom the outside after performing this operation, and a metal portion 32made of a metallic material and provided on an inner surface of theceramic portion 31.

The crown restoration 3 of this configuration exhibits good appearanceat the end of the operation and is capable of improving occlusion andreliably preventing occurrence of a crack or other defects in the crownrestoration 3.

Examples of the ceramic of which the ceramic portion 31 is made includesilicon oxide (silica), aluminum oxide (alumina), calcium oxide, sodiumoxide, potassium oxide, boron oxide, zinc oxide, magnesium oxide(magnesia), lithium oxide, tin oxide, indium oxide and titanium oxide.

On the other hand, the metallic material of which the metal portion 32is made has a composition different from that of the constituentmaterial of the titanium member 21. In general, gold or gold alloy isused as the metallic material.

If the metal portion 32 is made of gold or gold alloy, effects ofimproving occlusion and preventing occurrence of a crack or otherdefects in the crown restoration 3 become more conspicuous.

The crown restoration 3 is capped on the abutment 2 so that the metalportion 32 makes contact with the metal bonding surface 224 of theceramic member 22. Although the metal portion 32 comes into contact withthe ceramic member 22 (the metal bonding surface 224) at this time, itdoes not make contact with the titanium member 21 and the fixture 1. Ifdesired, it may be possible to use dental cement in bonding the abutment2 and the crown restoration 3 together.

In the case where the gum 60 is incised during the abutment couplingprocess, it is general that this process of capping the crownrestoration 3 is not performed until disappearance of tumescence of thegum 60 is confirmed over a time period of about 1 to 6 weeks after theabutment coupling process.

Dental Implant Manufacturing Method

Next, description will be made on a method for manufacturing the dentalimplant 10 set forth above.

Titanium Molded Body Production Step

First, a titanium molded body 21′ is obtained by molding a titaniummolded body composition that contains powder composed of titanium ortitanium alloy and a binder (see FIG. 3A). In the present embodiment,the titanium molded body 21′ is formed to have a protrusion 212′.

Hereinafter, the titanium molded body composition will be described indetail.

Powder

An average particle size of powder (metal powder) of which the titaniummolded body composition is composed is not particularly limited to aspecific value, but is preferably in the range of 0.3 to 100 μm, andmore preferably in the range of 0.5 to 50 μm.

If the average particle size of the powder falls within the range notedabove, it becomes possible to produce the titanium molded body 21′ andthe titanium member (sintered body) 21 with increased moldability (easeof molding), wherein the titanium member 21 is produced by degreasingand sintering the titanium molded body 21′.

It is also possible to increase density of the titanium member 21 thusobtained and to improve properties of the sintered body such asmechanical strength, dimensional accuracy and the like.

In contrast, if the average particle size of the powder is smaller thanthe lower limit value noted above, moldability of the titanium moldedbody 21′ exhibits a decrease. If the average particle size of the powderexceeds the upper limit value noted above, it is difficult tosufficiently increase density of the titanium member 21, which maypossibly lead to deterioration in properties of the titanium member 21.

The term “average particle size” used herein refers to a particle sizeof powder distributed at a point of 50% in terms of an accumulatedvolume in a particle size distribution of subject powder.

Although the power may be produced by any method, it is possible to usepowder obtained by, e.g., various kinds of atomizing methods including aliquid atomizing method such as a water-atomizing method or the like(e.g., a fast-rotating water stream atomizing method and arotating-liquid atomizing method) and a gas atomizing method, apulverizing method, a hydrogenation method and ahydrogenation-dehydrogenation method.

A content percentage of the powder contained in the titanium molded bodycomposition used in producing the titanium molded body 21′ having theprotrusion 212′ (a content percentage of the powder contained in thetitanium molded body 21′) is not particularly limited to a specificvalue.

It is preferred that the content percentage of the powder contained inthe titanium molded body composition is greater than a contentpercentage of powder contained in a ceramic molded body composition (aceramic molded body composition used in producing a ceramic molded body22′ having a recess 222′) as mentioned below, that is, a contentpercentage of powder contained in the ceramic molded body 22′.

This ensures that a content percentage of the binder contained in thetitanium molded body composition (the titanium molded body 21′) is keptrelatively small and further that the content percentage of the bindercontained in the titanium molded body composition (the titanium moldedbody 21′) is smaller than a content percentage of a binder contained inthe ceramic molded body composition.

Therefore, it is possible to control shrinkage of molded bodies in adegreasing step mentioned below, and to control shrinkage of degreasedbodies in a sintering step mentioned below, so that the shrinkage(contraction) of the titanium molded body 21′ can become smaller thanthat of the ceramic molded body 22′.

In other words, in the degreasing and sintering steps, when the moldedbodies (an assembled body which will be described below) are degreasedand sintered, the ceramic molded body 22′ (the molded body having therecess) can contract greater than the titanium molded body 21′ (themolded body having the protrusion).

As a result, it is possible to greatly increase adhesion and fixingstrength between the titanium member 21 (having the protrusion 212) andthe ceramic member 22 (having the recess 222) of the abutment 2 finallyobtained.

The concrete value of the content percentage of the powder contained inthe titanium molded body composition (the titanium molded body 21′) ispreferably in the range of 65 to 97 wt %, and more preferably in therange of 68 to 95 wt %.

If the content percentage of the powder is smaller than the lower limitvalue noted above, it is likely that the titanium member 21 obtainedexhibits reduction in its mechanical strength and dimensional stability.Furthermore, it may possibly become difficult to sufficiently increasefixing strength of the titanium member 21 relative to the ceramic member22 in the abutment 2 finally obtained.

In contrast, if the content percentage of the powder exceeds the upperlimit value noted above, the content percentage of the below-mentionedbinder is reduced correspondingly. Thus, the titanium molded bodycomposition exhibits reduced flowability during the molding process,which may possibly reduce operability.

Binder

The binder is a component that heavily affects moldability (ease ofmolding) of the titanium molded body composition and stability in shape(shape-keeping ability) of the titanium molded body 21′ and a titaniumdegreased body 21″ which is obtained by degreasing the titanium moldedbody 21′ as mentioned below.

If the titanium molded body composition contains such a component, itbecomes possible to easily and reliably produce the titanium member 21as a sintered body with increased dimensional accuracy.

Examples of the binder include: various kinds of resin such aspolyolefin (e.g., polyethylene, polypropylene and ethylene-vinyl acetatecopolymer), acrylic resin (e.g., polymethylmethacrylate andpolybuthylmethacrylate), styrene-based resin (e.g., polystyrene),polyvinyl chloride, polyvinylidene chloride, polyamide, polyester (e.g.,polyethylene terephthalate and polybutylene terephthalate), polyether,polyvinyl alcohol, polypropylene carbonate or copolymer thereof; variouskinds of wax; paraffin; higher fatty acid (e.g., stearic acid); higheralcohol; higher fatty acid ester; higher fatty acid amide; and the like.One or more of these substances may be used independently or incombination.

A content percentage of the binder contained in the titanium molded bodycomposition used in producing the titanium molded body 21′ having theprotrusion 212′ (a content percentage of the binder contained in thetitanium molded body 21′) is not particularly limited to a specificvalue.

It is preferred that the content percentage of the binder contained inthe titanium molded body composition is smaller than a contentpercentage of a binder contained in a ceramic molded body composition (aceramic molded body composition used in producing a ceramic molded body22′ having the recess 222′) as mentioned below, that is, a contentpercentage of a binder contained in the ceramic molded body 22′.

This makes it possible to control shrinkage of molded bodies (degreasedbodies) in a sintering step mentioned below, so that the shrinkage ofthe titanium molded body 21′ can become smaller than that of the ceramicmolded body 22′.

As a result, it is possible to greatly increase adhesion and fixingstrength between the titanium member 21 (having the protrusion 212) andthe ceramic member 22 (having the recess 222) of the abutment 2 finallyobtained.

The concrete value of the content percentage of the binder contained inthe titanium molded body composition is preferably in the range of 3 to35 wt %, and more preferably in the range of 5 to 32 wt %.

If the content percentage of the binder is smaller than the lower limitvalue noted above, it is likely that the titanium molded bodycomposition exhibits reduced flowability during the molding process,which may possibly reduce operability.

In contrast, if the content percentage of the binder exceeds the upperlimit value noted above, there is a possibility that the titanium member21 obtained exhibits reduction in its mechanical strength anddimensional stability. Furthermore, it may possibly become difficult tosufficiently increase fixing strength of the titanium member 21 relativeto the ceramic member 22 in the abutment 2 finally obtained.

Other Components

Other components may be contained in the titanium molded bodycomposition in addition to the above-mentioned components. Examples ofsuch components include a dispersant (lubricant), a plasticizer and anantioxidant, one or more of which may be used independently or incombination. This allows the titanium molded body composition to exhibitfunctions inherent in the respective components.

If the titanium molded body composition contains the dispersant amongthese components, the dispersant adheres to the powder. This makes itpossible to improve dispersibility of the powder in the titanium moldedbody composition.

Consequently, the titanium degreased body 21″ and the titanium sinteredbody (titanium member 21) to be obtained in subsequent steps exhibitparticularly high uniform composition (constitution) and property ineach and every portion thereof.

If the titanium molded body composition contains the dispersant, it isalso possible to greatly improve flowability of the titanium molded bodycomposition when molding the titanium molded body 21′ and to increasemold-filling ability thereof. This makes it possible to more reliablyobtain a titanium molded body 21′ having uniform density.

Examples of the dispersant include: an anionic organic dispersant suchas higher fatty acid (e.g., stearic acid, distearic acid, tristearicacid, linolenic acid, octanoic acid, oleic acid, palmitic acid andnaphthenic acid), polyacrylic acid, polymethacrylic acid, polymaleicacid, acrylic acid-maleic acid copolymer or polystyrene sulfonic acid; acationic organic dispersant such as quaternary ammonium acid; anon-ionic organic dispersant such as polyvinyl alcohol, carboxymethylcellulose or polyethylene glycol; an inorganic dispersant such astricalcium phosphate; and the like.

Among the above-noted substances, it is preferred that the dispersant iscomposed of the higher fatty acid as a major component thereof. This isbecause the higher fatty acid exhibits particularly high powderdispersibility.

Furthermore, a carbon number of the higher fatty acid is preferably inthe range of 16 to 30, and more preferably in the range of 16 to 24. Ifthe carbon number of the higher fatty acid falls within the above range,the titanium molded body composition exhibits improved shape-keepingability with no reduction in moldability.

Additionally, if the carbon number of the higher fatty acid falls withinthe above range, the higher fatty acid can be easily decomposed at arelatively low temperature.

If the titanium molded body composition contains the plasticizer, itbecomes possible to greatly improve plasticity and moldability of thetitanium molded body composition. As a result, it is possible toincrease mold-filling ability and to more reliably obtain a titaniummolded body 21′ having uniform density.

Examples of the plasticizer include phthalic acid ester (e.g., DOP, DEPand DBP), adipic acid ester, trimellitic acid ester, sebacic acid esterand the like.

The antioxidant has a function of preventing oxidation of resin of whichthe binder is composed. Examples of the antioxidant include a hinderedphenol-based antioxidant, hydrazine-based antioxidant, and the like.

The titanium molded body composition containing the respectivecomponents set forth above can be prepared by, e.g., mixing variouskinds of powder corresponding to the components.

If desired, kneading may be performed after the various kinds of powderare mixed. This makes it possible to increase flowability of thetitanium molded body composition and to improve homogeneity thereof.

Therefore, it is possible to obtain a titanium molded body 21′ havinghigher density and sufficient homogeneity. As a result, dimensionalaccuracy of the titanium degreased body 21″ and the titanium sinteredbody (the titanium member 21) can be improved.

The kneading of the mixture can be performed by various kinds ofkneading machines such as a pressure type or dual-arm kneader typekneading machine, a roller type kneading machine, a Banbury typekneading machine, and a single-axis or dual-axis extruding machine.

Kneading conditions depend on the particle size of the powder used, thecomposition of the binder, the blending quantity of the powder and thebinder and so forth. As an example, the kneading condition can be set toa condition in that a kneading temperature is in the range of 50 to 200°C. and a kneading time is in the range of 15 to 210 minutes.

If necessary, a kneaded product (compound) obtained is pulverized intopellets (small masses). A diameter of pellets may be set to the range ofabout 1 to 10 mm. A pulverizing device such as a pelletizer or the likecan be used in pelletizing the kneaded product.

The titanium molded body 21′ (a non-sintered body of the titanium member21) is obtained by molding the titanium molded body composition throughuse of a required molding method. Although the molding method of thetitanium molded body 21′ is not particularly limited to a specificmethod, an injection molding method is generally used because thetitanium molded body 21′ to be molded has a small size and a complexshape.

At the end of the injection molding process, the molded body thusobtained may be subjected to machining, electric discharging, laserprocessing, etching and so forth in order to remove burrs or to form aminute structure such as a groove or the like.

The molded body obtained by use of the titanium molded body compositioncontains the binder in a relatively high content percentage. Therefore,the molded body is easier to process than the titanium degreased body21″ and the titanium sintered body (the titanium member 21) which willbe set forth below. This means that the molded body can be easilysubjected to the above processing.

The titanium molded body 21′ obtained in this step has a protrusion 212′with a shape corresponding to that of the protrusion 212 of the titaniummember 21. Just like the protrusion 212 described earlier, it ispreferred that the protrusion 212′ of the titanium molded body 21′ has aportion whose cross-sectional shape is non-circular.

This makes it possible to more reliably prevent the titanium member 21and the ceramic member 22 of the finally obtained abutment 2 from makingrelative rotational movement. It is also possible to more effectivelyprevent any mismatching when the dental implant 10 is fixed in place.

Furthermore, the titanium molded body 21′ has a cross-sectional areaincreasing portion 213′ (with a cross-sectional area increasing from abase end toward a distal end thereof) that corresponds in shape to thecross-sectional area increasing portion 213 of the titanium member 21.

It is preferred that the cross-sectional area increasing portion 213′should satisfy the same conditions as applied to the cross-sectionalarea increasing portion 213 set forth earlier.

In other words, although the cross-sectional area increasing portion213′ may be formed in such a manner that the cross-sectional area of theprotrusion 212′ is increased either continuously or non-continuouslytoward the distal end thereof, it is preferred that the cross-sectionalarea is increased continuously.

An angle θ between a surface (a circumferential surface) of thecross-sectional area increasing portion 213′ and a heightwise axis ofthe protrusion 212′ is not particularly limited to a specific value, butis preferably in the range of 0.3 to 5°, and more preferably in therange of 1 to 40.

Moreover, it is preferred that the cross-sectional area increasingportion 213′ is formed over a full heightwise length of the protrusion212′.

Ceramic Molded Body Production Step

A ceramic molded body 22′ is obtained by molding a ceramic molded bodycomposition that contains powder composed of oxide-based ceramic and abinder (see FIG. 3B). In the present embodiment, the ceramic molded body22′ is formed to have a recess 222′.

Hereinafter, the ceramic molded body composition will be described indetail.

Powder

An average particle size of powder (oxide-based ceramic powder) of whichthe ceramic molded body composition is composed is not particularlylimited to a specific value, but is preferably in the range of 0.3 to100 μm, and more preferably in the range of 0.5 to 50 μm.

If the average particle size of the powder falls within the range notedabove, it becomes possible to produce the ceramic molded body 22′ andthe ceramic member (sintered body) 22 with increased moldability (easeof molding), wherein the ceramic member 22 is produced by degreasing andsintering the ceramic molded body 22′.

It is also possible to increase density of the ceramic member 22 thusobtained and to improve properties of the sintered body such asmechanical strength, dimensional accuracy and the like.

In contrast, if the average particle size of the powder is smaller thanthe lower limit value noted above, moldability of the ceramic moldedbody 22′ exhibits a decrease. If the average particle size of the powderexceeds the upper limit value noted above, it is difficult tosufficiently increase density of the ceramic member 22, which maypossibly lead to deterioration in properties of the ceramic member 22.

Although such powder may be produced by any method, it is possible touse powder obtained by, e.g., a gas-phase reaction method, a pulverizingmethod, a co-precipitation method, a hydrolysis control method, anemulsion method and a sol-gel method.

A content percentage of the powder contained in the ceramic molded bodycomposition used in producing the ceramic molded body 22′ having arecess 222′ (a content percentage of the powder contained in the ceramicmolded body 22′) is not particularly limited to a specific value.

It is preferred that the content percentage of the powder contained inthe ceramic molded body composition is smaller than the contentpercentage of the powder contained in the above-mentioned titaniummolded body composition (the titanium molded body composition used inproducing the titanium molded body 21′ having the protrusion 212′), thatis, the content percentage of the powder contained in the titaniummolded body 21′.

This ensures that the content percentage of the binder contained in theceramic molded body composition (the ceramic molded body 22′) is keptrelatively high and further that the content percentage of the bindercontained in the ceramic molded body composition (the ceramic moldedbody 22′) is greater than the content percentage of the binder containedin the titanium molded body composition (the titanium molded body 21′).

Therefore, it is possible to control shrinkage of molded bodies(degreased bodies) in a sintering step mentioned below, so that theshrinkage of the ceramic molded body 22′ can become greater than that ofthe titanium molded body 21′.

As a result, it is possible to sufficiently improve dimensional accuracyof the abutment 2 finally obtained and to greatly increase adhesion andfixing strength between the titanium member 21 (having the protrusion212) and the ceramic member 22 (having the recess 222).

The concrete value of the content percentage of the powder contained inthe ceramic molded body composition (the ceramic molded body 22′) is inthe range of preferably 60 to 94 wt %, and more preferably in the rangeof 65 to 92 wt %.

If the content percentage of the powder is smaller than the lower limitvalue noted above, it is likely that the ceramic member 22 obtainedexhibits reduction in its mechanical strength and dimensional stability.

In contrast, if the content percentage of the powder exceeds the upperlimit value noted above, the content percentage of the below-mentionedbinder is reduced correspondingly. Thus, the ceramic molded bodycomposition exhibits reduced flowability during the molding process,which may possibly reduce operability.

Furthermore, it may possibly become difficult to sufficiently increasefixing strength of the ceramic member 22 relative to the titanium member21 in the abutment 2 finally obtained.

Binder

The binder is a component that heavily affects moldability (ease ofmolding) of the ceramic molded body composition and stability in shape(shape-keeping ability) of the ceramic molded body 22′ and a ceramicdegreased body 22″ which is obtained by degreasing the ceramic moldedbody 22′ as mentioned below.

If the ceramic molded body composition contains such a component, itbecomes possible to easily and reliably produce the ceramic member 22 asa sintered body with increased dimensional accuracy.

As the binder of the ceramic molded body composition, it is possible touse the substances cited above as examples of the binder of the titaniummolded body composition.

A content percentage of the binder contained in the ceramic molded bodycomposition used in producing the ceramic molded body 22′ having therecess 222′ (a content percentage of the binder contained in the ceramicmolded body 22′) is not particularly limited to a specific value.

It is preferred that the content percentage of the binder contained inthe ceramic molded body composition is greater than the contentpercentage of the binder contained in the above-mentioned titaniummolded body composition (the titanium molded body composition used inproducing the titanium molded body 21′ having the protrusion 212′), thatis, the content percentage of the binder contained in the titaniummolded body 21′.

This makes it possible to control shrinkage of molded bodies (degreasedbodies) in a sintering step mentioned below, so that the shrinkage ofthe titanium molded body 21′ can become smaller than that of the ceramicmolded body 22′.

As a result, it is possible to greatly increase adhesion and fixingstrength between the titanium member 21 (having the protrusion 212) andthe ceramic member 22 (having the recess 222) of the abutment 2 finallyobtained.

The content percentage of the binder contained in the ceramic moldedbody composition (the ceramic molded body 22′) is preferably in therange of 6 to 40 wt %, and more preferably in the range of 8 to 35 wt %.

If the content percentage of the binder is smaller than the lower limitvalue noted above, it is likely that the ceramic molded body compositionexhibits reduced flowability during the molding process, which maypossibly reduce operability.

Furthermore, it may possibly become difficult to sufficiently increasefixing strength of the ceramic member 22 relative to the titanium member21 in the abutment 2 finally obtained.

In contrast, if the content percentage of the binder exceeds the upperlimit value noted above, there is a possibility that the ceramic member22 obtained exhibits reduction in its mechanical strength anddimensional stability.

In this regard, in the case where the content percentage of the bindercontained in the ceramic molded body 22′ (the molded body having therecess) is defined by C_(A) (wt %) and the content percentage of thebinder contained in the titanium molded body 21′ (the molded body withthe protrusion) is defined by C_(B) (wt %), C_(A) and C_(B) satisfypreferably a relation of 3≦C_(A)−C_(B)≦15, and more preferably arelation of 4≦C_(A)−C_(B)≦12.

If the C_(A) and C_(B) satisfy the above relation, the ceramic moldedbody 22′ can contract sufficiently greater than the titanium molded body21′. Therefore, it becomes possible to greatly increase adhesion andfixing strength between the titanium member 21 and the ceramic member 22in the dental implant 10 finally obtained.

Further, it is also possible to effectively prevent the titanium moldedbody 21′ and the ceramic molded body 22′ from undergoing inadvertentdeformation in the degreasing process. As a result, it is possible togreatly improve mechanical stability and dimensional accuracy of thedental implant 10 finally obtained.

Other Components

Other components may be contained in the ceramic molded body compositionin addition to the above-mentioned components. As these components, itis possible to use the substances cited above as examples of thecomponents of the titanium molded body composition. The same effects asdescribed above can be obtained by doing so.

The ceramic molded body composition containing the respective componentsset forth above can be prepared by, e.g., mixing various kinds of powdercorresponding to the components.

If desired, kneading may be performed after the various kinds of powderare mixed. This makes it possible to increase flowability of the ceramicmolded body composition and to improve homogeneity of the composition.

Therefore, it is possible to increase density and homogeneity of theceramic molded body 22′ and to improve dimensional accuracy of theceramic molded body 22′ and the ceramic sintered body (the ceramicmember 22).

The kneading of the mixture can be performed by the same method andunder the same conditions as described above in connection with thetitanium molded body composition.

The ceramic molded body 22′ (a non-sintered body of the ceramic member22) is obtained by molding the ceramic molded body composition throughuse of a required molding method.

Although the molding method of the ceramic molded body 22′ is notparticularly limited to a specific method, an injection molding methodis generally used because the ceramic molded body 22′ to be molded has asmall size and a complex shape.

At the end of the injection molding process, the molded body thusobtained may be subjected to machining, laser processing, etching and soforth in order to remove burrs or to form a minute structure such as agroove or the like.

The molded body obtained by use of the ceramic molded body compositioncontains the binder in a relatively high content percentage. Therefore,the molded body is easier to process than the ceramic degreased body 22″and the ceramic sintered body (the ceramic member 22) which will be setforth below. This means that the molded body can be easily subjected tothe above processing.

Assembling Step

Next, the titanium molded body 21′ and the ceramic molded body 22′obtained in the above manner are assembled together to obtain anassembled body (see FIG. 3C).

In the present step, the titanium molded body 21′ and the ceramic moldedbody 22′ are assembled together by inserting the protrusion 212′ of thetitanium molded body 21′ (corresponding to the protrusion 212 of thetitanium member 21) into the recess 222′ of the ceramic molded body 22′(corresponding to the recess 222 of the ceramic member 22) asillustrated in FIG. 4A.

A clearance with a sufficiently great width exists between theprotrusion (a non-contracted protrusion) 212′ of the titanium moldedbody 21′ and the recess (a non-contracted recess) 222′ of the ceramicmolded body 22′. This reliably prevents the titanium molded body 21′ andthe ceramic molded body 22′ from undergoing inadvertent deformation,e.g., when the protrusion 212′ is inserted into the recess 222′.

Degreasing Step

Next, the assembled body formed of the titanium molded body 21′ and theceramic molded body 22′ is subjected to a degreasing process. By doingso, the binder contained in the titanium molded body 21′ is removedtherefrom to transform the titanium molded body 21′ into a titaniumdegreased body 21″, and the binder contained in the ceramic molded body22′ is removed therefrom to transform the ceramic molded body 22′ into aceramic degreased body 22″ (see FIG. 3D).

A method for the degreasing process is not particularly limited to aspecific method. Examples of the method for the degreasing processinclude a heat treatment either in a non-oxidant atmosphere, e.g., in avacuum or depressurized state (of, e.g., 1×10⁻¹ to 1×10⁻⁶ Torr or 13.3to 1.33×10⁻⁴ Pa) or under the presence of a gas such as a nitrogen gas,an argon gas and the like.

A processing temperature in the degreasing (heat treatment) step is notparticularly limited to a specific value, but is preferably in the rangeof 100 to 780° C., and more preferably in the range of 150 to 720° C.

Further, a processing (heat treatment) time in the degreasing (heattreatment) step is not particularly limited to a specific value, but ispreferably in the range of 0.5 to 20 hours, and more preferably in therange of 1 to 10 hours.

In this regard, it is to be noted that the degreasing process using theheat treatment may be performed through a plurality of steps fordifferent purposes (e.g., for the purpose of shortening the degreasingtime).

In this case, it may be possible to use, e.g., a method by which aformer half of the degreasing process is performed at a low temperatureand a latter half of the degreasing process is performed at a hightemperature, a method by which a low-temperature degreasing process anda high-temperature degreasing process are performed alternately, or thelike.

In the case where the titanium molded body 21′ and the ceramic moldedbody 22′ are composed of different materials containing differentbinders from each other, it may be possible to perform a firstdegreasing process in such a condition that the binder is preferentiallyremoved from one molded body (the molded body containing a binderremovable at a lower temperature) and then perform a second degreasingprocess in such a condition that the binder is preferentially removedfrom the other molded body (the molded body containing a binderremovable at a higher temperature).

At the end of the degreasing process, the assembled body including thetitanium degreased body 21″ and the ceramic degreased body 22″ may besubjected to machining, electric discharging, laser processing, etchingand so forth in order to remove burrs or to form a minute structure suchas a groove or the like.

The degreased bodies (the titanium degreased body 21″ and the ceramicdegreased body 22″) are easier to process than the sintered bodies (thetitanium member 21 and the ceramic member 22).

In this regard, it is to be noted that the binders contained in themolded bodies (the titanium molded body 21′ and the ceramic molded body22′) may not be completely removed therefrom in this step. In this case,it is possible to suitably remove the residual binders in the followingsintering step.

Sintering Step

Next, the assembled body thus degreased is subjected to a sinteringprocess, whereby the titanium degreased body 21″ (a non-sintered body ofthe titanium member 21) is transformed into the titanium member(sintered body) 21 and the ceramic degreased body 22″ (a non-sinteredbody of the ceramic member 22) is transformed into the ceramic member(sintered body) 22.

Thus, the titanium member 21 is firmly fixed and joined to the ceramicmember 22 (see FIG. 3E). This provides the abutment 2 in which thetitanium member 21 and the ceramic member 22 are fixedly joinedtogether.

As described above, one of the features of the present invention residesin that the titanium member is firmly fixed and joined to the ceramicmember by subjecting the assembled body consisting of the titaniummolded body and the ceramic molded body to the degreasing process andthe sintering process.

Alternatively, it would be conceivable that a ceramic member and atitanium member are independently produced and bonded together by useof, e.g., dental cement. However, in general, titanium or titanium alloyexhibits inferior bondability (adhesiveness) with respect to ceramic.Therefore, if the ceramic member and the titanium member are merelybonded together by the use of the dental cement, it is impossible toattain sufficiently high bonding strength. It is also likely that adental implant is destroyed after its application to a living body.

As a further alternative, it would be conceivable that an adhesive agentstronger than the generally available dental cement is used in bonding aceramic member and a titanium member together. In this case, however,there exists a hazard that a component contained in the adhesive agentmay adversely affect the living body to which a dental implant isapplied.

The titanium member 21 and the ceramic member 22 are formed due tocontraction of the molded bodies through the degreasing process and thesintering process. As a result of this contraction, the protrusion (acontracted protrusion) 212 of the titanium member 21 is in close contactwith and fitted to the recess (a contracted recess) 222 of the ceramicmember 22.

In other words, a clearance that has existed between the titanium moldedbody 21′ (the protrusion 212′) and the ceramic molded body 22′ (therecess 222′) in the assembling process thereof is eliminated bydegreasing and sintering the titanium molded body 21′ and the ceramicmolded body 22′, thereby bringing the titanium member 21 into closecontact with the ceramic member 22.

Consequently, the titanium member 21 is firmly fixed to the ceramicmember 22 so that the titanium member 21 and the ceramic member 22 canbe kept in an inseparable state.

Particularly, the titanium molded body 21′ used in the presentembodiment has the cross-sectional area increasing portion 213′ setforth above and the resultant titanium member 21 has the cross-sectionalarea increasing portion 213.

Therefore, even if a relatively great tensile force is imparted in adirection parallel to a direction of depth of the recess 222 (adirection of a height of the protrusion 212), it is possible to keep thetitanium member 21 and the ceramic member 22 in a fixedly coupled state.

In addition, if the content percentage of the binder contained in thetitanium molded body 21′ (the molded body having the protrusion) and thecontent percentage of the binder contained in the ceramic molded body22′ (the molded body having the recess) are set to satisfy the relationmentioned earlier, the titanium member 21 is more firmly fixed andjoined to the ceramic member 22, thereby increasing mechanical stabilityof the dental implant.

In the present embodiment, the following effects are attained becausethe titanium molded body 21′ has the protrusion 212′ and the ceramicmolded body 22′ has the recess 222′.

In general, oxide-based ceramic of which the ceramic molded body 22′ iscomposed has a melting point higher than that of titanium or titaniumalloy. For this reason, the ceramic member 22 (the ceramic degreasedbody 22″) is less deformable than the titanium member 21 (the titaniumdegreased body 21″) in the sintering step, while the titanium member 21(the titanium degreased body 21″) undergoes suitable deformation.

The protrusion 212 of the titanium member 21 conforms in shape to therecess 222 of the ceramic member 22, whereby adhesion between theprotrusion 212 and the recess 222 grows extremely high. This greatlyimproves mechanical stability of the dental implant (the abutment 2)obtained.

Although the titanium member 21 is more easily deformed than the ceramicmember 22 in the sintering step, it is possible to reliably prevent thetitanium member 21 from undergoing any involuntary deformation in thetemperature range described above.

A method for the sintering process is not particularly limited to aspecific method. Examples of the method for the sintering processinclude a heat treatment either in a non-oxidant atmosphere, e.g., in avacuum or depressurized state (of, e.g., 1×10⁻² to 1×10⁻⁶ Torr or 133 to1.33×10⁻⁴ Pa) or under the presence of a gas such as a nitrogen gas, anargon gas and the like.

The atmosphere in which the sintering step is performed may be changedin the midst of the step. For example, the sintering atmosphere may be adepressurized atmosphere at the outset and may be changed to an inertatmosphere in the middle of the sintering step.

Furthermore, the sintering step may be divided into two or more steps.This makes it possible to improve sintering efficiency and to shorten asintering time.

It is preferred that the sintering step is performed just after thedegreasing step. This allows the degreasing step to serve as apre-sintering step in which the degreased bodies (the titanium degreasedbody 21″ and the ceramic degreased body 22″) are pre-heated. Thisensures that the degreased bodies are sintered in a reliable manner.

A processing temperature in the sintering (heat treatment) step is notparticularly limited to a specific value, but is preferably in the rangeof 1000 to 1500° C., and more preferably in the range of 1050 to 1450°C.

If the processing temperature falls within the above-noted range, it ispossible to prevent any inadvertent deformation during the sinteringstep and also to reliably obtain an abutment 2 in which the titaniummember 21 and the ceramic member 22 are more firmly fixed and joinedtogether.

A processing (heat treatment) time in the sintering (heat treatment)step is preferably in the range of 0.5 to 20 hours, and more preferablyin the range of 1 to 15 hours.

In this regard, it is to be noted that the degreasing process using theheat treatment may be performed through a plurality of steps fordifferent purposes (e.g., for the purpose of shortening the sinteringtime).

In this case, it may be possible to use, e.g., a method by which aformer half of the sintering process is performed at a low temperatureand a latter half of the sintering process is performed at a hightemperature or a method by which a low-temperature sintering process anda high-temperature sintering process are performed alternately.

At the end of the sintering process, the sintered bodies thus obtainedmay be subjected to machining, electric discharging, laser processing,etching and so forth in order to remove burrs or to form a minutestructure such as a groove or the like.

As compared to the molded bodies (the titanium molded body 21′ and theceramic molded body 22′) and the degreased bodies (the titaniumdegreased body 21″ and the ceramic degreased body 22″), the sinteredbodies are closer in shape and size to the members to be produced (thetitanium member 21 and the ceramic member 22).

This means that dimensional accuracy of the abutment 2 (the titaniummember 21 and the ceramic member 22) finally obtained by processing thesintered bodies is greater than that of the abutment 2 produced bysubjecting the molded bodies or the degreased bodies to machining,electric discharging, laser processing, etching and so forth.

Production of Fixture

The fixture 1 is produced independently of the production of theabutment 2. A method of producing the fixture 1 is not particularlylimited to a specific method.

It is preferred that the fixture 1 is produced by a method whichincludes a molding step (a molded fixture body production step) formolding a molded body composition containing powder composed of aconstituent material of the fixture 1 and a binder to obtain a moldedfixture body, a degreasing step (a molded fixture body degreasing step)for degreasing the molded fixture body by removing the binder containedin the molded fixture body therefrom to transform it into a degreasedfixture body, and a sintering step (a degreased fixture body sinteringstep) for sintering the degreased fixture body.

Use of this method makes it possible to easily and accurately producethe fixture 1 even if the fixture 1 is of the type used in the dentalimplant 10 having a minute structure. In the case where the fixture 1 isproduced by the above method, it is possible to produce the moldedfixture body in the same manner as available in molding the titaniummolded body described earlier.

Furthermore, the degreasing process and the subsequent sintering processfor the molded fixture body can be performed by the same method and inthe same conditions as described above with regard to the degreasingstep (for the assembled body) and the sintering step (for the assembledbody).

The dental implant 10 is obtained by producing the fixture 1 and theabutment 2 in the above-described manner (see FIG. 3F).

While a preferred embodiment of the present invention has been describedabove, the present invention is not limited thereto. For example, anarbitrary step may be optionally added to the method of manufacturingthe dental implant (particularly, the abutment).

Furthermore, although the dental implant includes the fixture and theabutment in the embodiment described above, it may have other structuresas long as the titanium member and the ceramic member are fixed togetherin the above-mentioned manner. As an example, the dental implant of thepresent invention may be comprised of only the titanium member and theceramic member.

Moreover, although the titanium molded body (the titanium member) hasthe protrusion and the ceramic molded body (the ceramic member) has therecess in the embodiment described above, the titanium molded body (thetitanium member) may be modified to have a recess and the ceramic moldedbody (the ceramic member) may be modified to have a protrusion.

Furthermore, at least one of the titanium molded body (the titaniummember) and the ceramic molded body (the ceramic member) may not beprovided with the protrusion or the recess. In addition, although theabutment is comprised of two members in the embodiment described above,it may include three or more members.

EXAMPLES

Next, description will be made on specific examples of the presentinvention.

1. Manufacture of Dental Implant

Example 1 1-1. Production of Fixture

Prepared first was titanium powder with an average particle size of 20μm, which was produced by a gas atomizing method.

A binder composed of 2.7 wt % of polystyrene (PS), 2.7 wt % ofethylene-vinyl acetate copolymer (EVA) and 2.3 wt % of paraffin wax and1.3 wt % of dibutylphthalate (plasticizer) were mixed with 91 wt % ofthe titanium powder to obtain a mixture.

The mixture was kneaded by a pressure type kneader (kneading machine)under the conditions of a kneading temperature of 100° C. and a kneadingtime of 60 min to obtain a kneaded product. This kneading was carriedout in a nitrogen atmosphere.

Next, the kneaded product was pulverized into pellets with an averageparticle size of 3 mm. The pellets were put into an injection moldingmachine, and injected into a mold provided in the machine and having aninternal shape corresponding to an external shape of the fixture to beproduced under the molding conditions of a material temperature of 130°C. and an injection pressure of 10.8 MPa (110 kgf/cm²) to obtain amolded fixture body within the mold. Thereafter, the molded fixture bodywas ejected from the mold. This process was repeatedly performed toobtain a specified number of the molded fixture bodies.

The molded fixture bodies thus obtained were degreased under theconditions of a degreasing temperature of 450° C., a degreasing time ofone hour and a degreasing atmosphere of nitrogen gas (set to theatmospheric pressure), so that the binder contained in the moldedfixture bodies was removed therefrom to transform them into degreasedfixture bodies.

Then, under the conditions of a sintering temperature of 1200° C., asintering time of three hours and a vacuum sintering atmosphere, thedegreased fixture bodies were sintered to obtain sintered bodies.

Subsequently, the sintered bodies thus obtained were machined so thatcutout portions (see FIG. 1A) were formed to produce fixtures asdesired.

1-2. Production of Abutment

Titanium Molded Body Production Step

Prepared first was titanium powder with an average particle size of 20μm, which was produced by a gas atomizing method.

A binder composed of 2.7 wt % of polystyrene (PS), 2.7 wt % ofethylene-vinyl acetate copolymer (EVA) and 2.3 wt % of paraffin wax and1.3 wt % of dibutylphthalate (plasticizer) were mixed with 91 wt % ofthe titanium powder to obtain a mixture.

The mixture was kneaded by a pressure type kneader (kneading machine)under the conditions of a kneading temperature of 100° C. and a kneadingtime of 60 min to obtain a kneaded product. The kneading was carried outin a nitrogen atmosphere.

Next, the kneaded product was pulverized into pellets with an averageparticle size of 5 mm. The pellets were put into an injection moldingmachine, and injected into a mold provided in the machine and having aninternal shape corresponding to an external shape of the titanium memberto be produced under the molding conditions of a material temperature of130° C. and an injection pressure of 10.8 MPa (110 kgf/cm²) to obtain atitanium molded body within the mold. At this time, the protrusion wasformed in the titanium molded body. Thereafter, the titanium molded bodyhaving the protrusion was ejected from the mold. This process wasrepeatedly performed to obtain a specified number of the titanium moldedbodies (see FIG. 3A).

Further, the titanium molded bodies thus obtained had the samecomposition ratio as that of the mixture (the composition) prepared atthe outset.

Each of the titanium molded bodies obtained in this manner had aprotrusion whose cross-sectional shape was non-circular (rectangular).Furthermore, each of the titanium molded bodies had a cross-sectionalarea increasing portion extending over a full heightwise length of theprotrusion.

An angle θ between a surface (circumference surface) of thecross-sectional area increasing portion and a heightwise axis of theprotrusion was 1.5°.

Ceramic Molded Body Production Step

Prepared first was zirconia powder with an average particle size of 0.5μm, which was produced by a co-precipitation method.

A binder composed of 4.8 wt % of polystyrene (PS), 3.8 wt % ofethylene-vinyl acetate copolymer (EVA) and 4.8 wt % of paraffin wax and2.6 wt % of dibutylphthalate (plasticizer) were mixed with 84 wt % ofthe zirconia powder to obtain a mixture.

The mixture was kneaded by a pressure type kneader (kneading machine)under the conditions of a kneading temperature of 100° C. and a kneadingtime of 60 min to obtain a kneaded product. The kneading was carried outin a nitrogen atmosphere.

Next, the kneaded product was pulverized into pellets with an averageparticle size of 3 mm. The pellets were put into an injection moldingmachine, and injected into a mold provided in the machine and having aninternal shape corresponding to an external shape of the ceramic memberto be produced under the molding conditions of a material temperature of140° C. and an injection pressure of 10.8 MPa (110 kgf/cm²) to obtain aceramic molded body within the mold. At this time, the recess was formedin the ceramic molded body. Thereafter, the ceramic molded body havingthe recess was ejected from the mold. This process was repeatedlyperformed to obtain a specified number of the ceramic molded bodies (seeFIG. 3B).

Further, the ceramic molded bodies thus obtained had the samecomposition ratio as that of the mixture (the composition) prepared atthe outset.

Assembling Step

Next, the titanium molded bodies and the ceramic molded bodies thusobtained were assembled together to obtain assembled bodies (see FIG.3C). At this time, the protrusion of each of the titanium molded bodieswas inserted into the recess of each of the ceramic molded bodies.

Degreasing Step

Next, the assembled bodies thus obtained were degreased under theconditions of a degreasing temperature of 450° C., a degreasing time oftwo hours and a degreasing atmosphere of nitrogen gas (set to theatmospheric pressure).

By doing so, the binder contained in the titanium molded bodies wasremoved therefrom to transform them into titanium degreased bodies, andthe binder contained in the ceramic molded bodies was removed therefromto transform them into ceramic degreased bodies (see FIG. 3D).

Sintering Step

Next, the titanium degreased bodies and the ceramic degreased bodiesthus obtained were sintered under the conditions of a sinteringtemperature of 1400° C., a sintering time of five hours and a sinteringatmosphere of argon gas (set to the atmospheric pressure).

By doing so, the titanium degreased bodies were transformed intotitanium members as sintered bodies, and the ceramic degreased bodieswere transformed into ceramic members as sintered bodies. Thus, thetitanium members were firmly fixed and joined to the ceramic members(see FIG. 3E).

Machining Step

Subsequently, the abutments as desired were obtained by machining thetitanium members and adjusting a shape of each of male thread portionsthereof. In the abutments thus obtained, the recess of each of theceramic members was fitted to the protrusion of each of the titaniummembers so that the titanium members and the ceramic members could bestrongly fixed and joined together.

Finally, dental implants were obtained by combining the fixtures and theabutments produced as above.

Examples 2 to 7

Dental implants were manufactured in the same manner as in Example 1,except that the composition ratio of the composition (the kneadedproduct) used in producing the abutments (the titanium members and theceramic members) was changed, that the same composition as that of thetitanium molded bodies was used as the composition (the kneaded product)for production of the fixtures, and that the production conditions ofthe abutments were changed as shown in Table 1.

Comparative Example 1

Dental implants were manufactured in the same manner as in Example 1,except that each of the abutments was produced in the form of anintegral titanium member having the same external shape as that of eachof the abutments produced in the foregoing examples.

Hereinbelow, an abutment production method according to this comparativeexample will be described in detail.

First, a binder composed of 2.7 wt % of polystyrene (PS), 2.7 wt % ofethylene-vinyl acetate copolymer (EVA) and 2.3 wt % of paraffin wax and1.3 wt % of dibutylphthalate (plasticizer) were mixed with 91 wt % oftitanium powder having an average particle size of 20 μm, which wasproduced by a gas atomizing method, to obtain a mixture.

The mixture was kneaded by a pressure type kneader (kneading machine)under the conditions of a kneading temperature of 100° C. and a kneadingtime of 60 min to obtain a kneaded product. The kneading was carried outin a nitrogen atmosphere.

Next, the kneaded product was pulverized into pellets with an averageparticle size of 5 mm. The pellets were put into an injection moldingmachine, and injected into a mold provided in the machine and having aninternal shape corresponding to an external shape of the abutment to beproduced under the molding conditions of a material temperature of 130°C. and an injection pressure of 10.8 MPa (110 kgf/cm²) to obtain amolded body within the mold. Thereafter, the molded body was ejectedfrom the mold. This process was repeatedly performed to obtain aspecified number of the molded bodies.

In this regard, it is to be noted that at this time, a size of each ofthe molded bodies was decided by taking into account shrinkage thereofwhich would occur in the subsequent degreasing and sintering steps.

Next, the molded bodies thus obtained were degreased under theconditions of a degreasing temperature of 450° C., a degreasing time ofone hour and a degreasing atmosphere of nitrogen gas (set to theatmospheric pressure). By doing so, the binder contained in the moldedbodies was removed therefrom to transform them into degreased bodies.

Then, the degreased bodies were sintered under the conditions of asintering temperature of 1200° C., a sintering time of three hours and asintering atmosphere of argon gas (set to the atmospheric pressure) toobtain sintered bodies.

Subsequently, the abutments as desired were obtained by machining thesintered bodies and adjusting a shape of each of male thread portionsthereof.

Comparative Example 2

Dental implants were manufactured in the same manner as in Example 1,except that each of the abutments was produced in the form of anintegral zirconia member having the same external shape as that of eachof the abutments produced in the foregoing examples.

Hereinbelow, an abutment production method according to this comparativeexample will be described in detail.

First, a binder composed of 4.8 wt % of polystyrene (PS), 3.8 wt % ofethylene-vinyl acetate copolymer (EVA) and 4.8 wt % of paraffin wax and2.6 wt % of dibutylphthalate (plasticizer) were mixed with 84 wt % ofzirconia powder having an average particle size of 0.5 μm, which wasproduced by a co-precipitation method, to obtain a mixture.

The mixture was kneaded by a pressure type kneader (kneading machine)under the conditions of a kneading temperature of 100° C. and a kneadingtime of 60 min to obtain a kneaded product. The kneading was carried outin a nitrogen atmosphere.

Next, the kneaded product was pulverized into pellets with an averageparticle size of 3 mm. The pellets were put into an injection moldingmachine, and injected into a mold provided in the machine and having aninternal shape corresponding to an external shape of the abutment to beproduced under the molding conditions of a material temperature of 140°C. and an injection pressure of 10.8 MPa (110 kgf/cm²) to obtain amolded body within the mold. Thereafter, the molded body was ejectedfrom the mold. This process was repeatedly performed to obtain aspecified number of the molded bodies.

In this regard, it is to be noted that at this time, a size of each ofthe molded bodies was decided by taking into account shrinkage whichwould occur in the subsequent degreasing and sintering steps.

Next, the molded bodies thus obtained were degreased under theconditions of a degreasing temperature of 500° C., a degreasing time oftwo hours and a degreasing atmosphere of nitrogen gas (set to theatmospheric pressure). By doing so, the binder contained in the moldedbodies was removed therefrom to transform them into degreased bodies.

Then, the degreased bodies were sintered under the conditions of asintering temperature of 1450° C., a sintering time of three hours and asintering atmosphere of air to obtain sintered bodies.

Subsequently, the abutments as desired were obtained by machining thesintered bodies and adjusting a shape of each of male thread portionsthereof.

Comparative Example 3

Dental implants were manufactured in the same manner as in Example 1,except that each of the abutments was produced by independentlyproducing and bonding titanium members (titanium sintered bodies) andceramic members (ceramic sintered bodies) with dental cement.

In this regard, it is to be noted that each of the abutments had thesame external shape as that of each of the abutments produced in theforegoing examples.

Hereinbelow, an abutment production method according to this comparativeexample will be described in detail.

Production of Titanium Members

First, a binder composed of 2.7 wt % of polystyrene (PS), 2.7 wt % ofethylene-vinyl acetate copolymer (EVA) and 2.3 wt % of paraffin wax and1.3 wt % of dibutylphthalate (plasticizer) were mixed with 91 wt % oftitanium powder having an average particle size of 20 μm, which wasproduced by a gas atomizing method, to obtain a mixture.

The mixture was kneaded by a pressure type kneader (kneading machine)under the conditions of a kneading temperature of 100° C. and a kneadingtime of 60 min to obtain a kneaded product. The kneading was carried outin a nitrogen atmosphere.

Next, the kneaded product was pulverized into pellets with an averageparticle size of 5 mm. The pellets were put into an injection moldingmachine, and injected into a mold provided in the machine and having aninternal shape corresponding to an external shape of a lower part of anabutment shown in FIG. 5 (a member to be threadedly coupled to thefixture) under the molding conditions of a material temperature of 130°C. and an injection pressure of 10.8 MPa (110 kgf/cm²) to obtain atitanium molded body within the mold. Thereafter, the titanium moldedbody was ejected from the mold. This process was repeatedly performed toobtain a specified number of the titanium molded bodies.

In this regard, it is to be noted that at this time, a size of each ofthe titanium molded bodies was decided by taking into account shrinkagewhich would occur in the subsequent degreasing and sintering steps.

Next, the titanium molded bodies thus obtained were degreased under theconditions of a degreasing temperature of 450° C., a degreasing time ofone hour and a degreasing atmosphere of nitrogen gas (set to theatmospheric pressure). By doing so, the binder contained in the titaniummolded bodies was removed therefrom to transform them into titaniumdegreased bodies.

Then, the titanium degreased bodies were sintered under the conditionsof a sintering temperature of 1200° C., a sintering time of three hoursand a sintering atmosphere of argon gas (set to the atmosphericpressure) to obtain titanium sintered bodies.

Subsequently, the titanium members as desired were obtained by machiningthe titanium sintered bodies and adjusting a shape of each of malethread portions thereof.

Production of Ceramic Members

First, a binder composed of 4.8 wt % of polystyrene (PS), 3.8 wt % ofethylene-vinyl acetate copolymer (EVA) and 4.8 wt % of paraffin wax and2.6 wt % of dibutylphthalate (plasticizer) were mixed with 84 wt % ofzirconia powder having an average particle size of 0.5 μm, which wasproduced by a co-precipitation method, to obtain a mixture.

The mixture was kneaded by a pressure type kneader (kneading machine)under the conditions of a kneading temperature of 100° C. and a kneadingtime of 60 min to obtain a kneaded product. The kneading was carried outin a nitrogen atmosphere.

Next, the kneaded product was pulverized into pellets with an averageparticle size of 3 mm. The pellets were put into an injection moldingmachine, and injected into a mold provided in the machine and having aninternal shape corresponding to an external shape of an upper part of anabutment shown in FIG. 5 (a member to be capped by a crown restoration)under the molding conditions of a material temperature of 140° C. and aninjection pressure of 10.8 MPa (110 kgf/cm²) to obtain a ceramic moldedbody within the mold. Thereafter, the ceramic molded body was ejectedfrom the mold. This process was repeatedly performed to obtain aspecified number of the ceramic molded bodies.

In this regard, it is to be noted that at this time, a size of each ofthe ceramic molded bodies was decided by taking into account shrinkagewhich would occur in the subsequent degreasing and sintering steps.

Next, the ceramic molded bodies thus obtained were degreased under theconditions of a degreasing temperature of 500° C., a degreasing time oftwo hours and a degreasing atmosphere of nitrogen gas (set to theatmospheric pressure). By doing so, the binder contained in the ceramicmolded bodies was removed therefrom to transform them into ceramicdegreased bodies.

Then, the ceramic degreased bodies were sintered under the conditions ofa sintering temperature of 1450° C., a sintering time of three hours anda sintering atmosphere of argon gas (set to the atmospheric pressure) toobtain ceramic members.

Bonding of Titanium Members and Ceramic Members (Completion ofAbutments)

Subsequently, abutments were produced by bonding the titanium members(the titanium sintered bodies) and the ceramic members (the ceramicsintered bodies) with dental cement (“Glass Ionomer”, produced by GCAmerica, Inc.).

The production conditions of the fixtures and the abutments employed inthe respective examples and the respective comparative examples arecollectively shown in Table 1. The configurations of the dental implantsmanufactured in the respective examples and the respective comparativeexamples are collectively shown in Table 2.

The symbol θ in Table 1 refers to the angle between the surface of thecross-sectional area increasing portion of the titanium molded body andthe heightwise axis of the protrusion of the titanium molded body.

The symbol θ in Table 2 refers to the angle between the surface of thecross-sectional area increasing portion of the titanium member and theheightwise axis of the protrusion of the titanium member.

Referring to Comparative Example 3 shown in Table 1, the processingconditions adopted in the degreasing step for the titanium molded bodiesare indicated in the upper line of the degreasing step column, and theprocessing conditions adopted in the degreasing step for the ceramicmolded bodies are indicated in the lower line of the degreasing stepcolumn.

Further, the processing conditions adopted in the sintering step for thetitanium degreased bodies are indicated in the upper line of thesintering step column, and the processing conditions adopted in thesintering step for the ceramic degreased bodies are indicated in thelower line of the sintering step column.

Referring to Comparative Examples 1 and 2 shown in Table 2, theconditions for the portion threadedly coupled to the fixture (theportion corresponding to the titanium member in the present invention)are indicated in the titanium member column, and the conditions for theportion capped by the crown restoration (the portion corresponding tothe ceramic member in the present invention) are indicated in theceramic member column.

TABLE 1 Ceramic Molded Body Titanium Molded Body Production StepProduction Step Ceramic Titanium Molded Body Molded Existence Body orNon- Content Content existence Percentage Percentage Protrusion ofCross- Material Injection [wt %] Material Injection [wt %] Cross-sectional Area Temperature Pressure Binder Temperature Pressure BinderHeight sectional Increasing θ [° C.] [MPa] Powder (C_(A)) [° C.] [MPa]Powder (C_(B)) [mm] Shape Portion [°] Ex. 1 140 10.8 84 13.4 130 10.8 917.7 4 Rectangle Existence 1.5 Ex. 2 140 10.8 84 13.4 130 10.8 91 7.7 4Rectangle Existence 1 Ex. 3 140 10.8 84 13.4 130 10.8 91 7.7 2 EllipsoidExistence 4 Ex. 4 140 10.8 84 13.4 130 10.8 91 7.7 5 Ellipsoid Existence1.5 Ex. 5 140 10.8 87 10.7 130 10.8 91 7.7 4 Rectangle Existence 1.5 Ex.6 140 10.8 77 19.2 130 10.8 95 4.2 4 Rectangle Existence 1.5 Ex. 7 14010.8 60 33.6 130 10.8 65 29.4 4 Rectangle Existence 1.5 Com. — — — — 13010.8 91 7.7 — — Non-existence — Ex. 1 Com. 140 10.8 84 13.4 — — — — — —Non-existence — Ex. 2 Com. 140 10.8 84 13.4 130 10.8 91 7.7 — —Non-existence — Ex. 3 Assembling Machining Step Degreasing SinteringStep Existence Step Step Existence or Non- Processing ProcessingProcessing Processing or Non- C_(A) − C_(B) existence of TemperatureTime Temperature Time existence of [wt %] This Step [° C.] [hours]Atmosphere [° C.] [hours] Atmosphere This Step Ex. 1 5.7 Existence 450 2N₂ 1400 5 Ar Existence Ex. 2 5.7 Existence 450 2 N₂ 1400 5 Ar ExistenceEx. 3 5.7 Existence 450 2 N₂ 1400 5 Ar Existence Ex. 4 5.7 Existence 4502 N₂ 1400 5 Ar Existence Ex. 5 3.0 Existence 450 2 N₂ 1400 5 ArExistence Ex. 6 15.0 Existence 450 2 N₂ 1400 5 Ar Existence Ex. 7 4.2Existence 450 2 N₂ 1400 5 Ar Existence Com. — Non-existence 450 1 N₂1200 3 Ar Existence Ex. 1 Com. — Non-existence 500 2 N₂ 1450 3 AirExistence Ex. 2 Com. — Non-existence 450 1 N₂ 1200 3 Ar Existence Ex. 3500 2 N₂ 1450 3 Ar Existence

TABLE 2 Configuration of Abutment Titanium Member Ceramic Existence orConfiguration Member Non-existence of of Fixture Constituent Depth ofConstituent Height of Cross-sectional Area θ Constituent Existence orNon-existence Material Recess [mm] Material Protrusion [mm] IncreasingPortion [°] Material of Cutout Portion Ex. 1 ZrO₂ 4.2 Ti 4 Existence 1.5Ti Existence Ex. 2 ZrO₂ 4.2 Ti 4 Existence 1 Ti Existence Ex. 3 ZrO₂ 2.1Ti 2 Existence 4 Ti Existence Ex. 4 ZrO₂ 5.2 Ti 5 Existence 1.5 TiExistence Ex. 5 ZrO₂ 4.2 Ti 4 Existence 1.5 Ti Existence Ex. 6 ZrO₂ 4.2Ti 4 Existence 1.5 Ti Existence Ex. 7 ZrO₂ 4.2 Ti 4 Existence 1.5 TiExistence Com. Ti — Ti — — — Ti Existence Ex. 1 Com. ZrO₂ — ZrO₂ — — —Ti Existence Ex. 2 Com. ZrO₂ 4.2 Ti 4 Non-existence — Ti Existence Ex. 3

2. Bonding of Crown Restoration

In a state that the fixture and the abutment of the dental implantobtained in each of the examples had been threadedly coupled together, acrown restoration was bonded by dental cement (“Superbond”, produced bySun Medical Ltd.) to a surface (a metal bonding surface shown in FIGS.1A to 1C) of the abutment opposite to a side on which the abutment wasthreadedly coupled to the fixture.

The crown restoration used was of a type including a metal layer made ofgold and arranged on an inner surface side (a surface facing theabutment) and a ceramic portion made of silicon oxide (silica) andaluminum oxide (alumina) and arranged on an outer surface side (asurface opposite to the abutment). Thereafter, the crown restoration wasfixed to the dental implant by hardening the dental cement.

With respect to the dental implant obtained in each of the comparativeexamples, a crown restoration was bonded by dental cement (“Superbond”,produced by Sun Medical Ltd.) to a portion corresponding to the metalbonding surface of the abutment obtained in each of the examples. Then,the dental cement was hardened.

3. Evaluation

3-1. Measurement of Elution Amount of Metal Ions

In respect of each of the dental implants of the examples and thecomparative examples to which the crown restorations were bonded in theabove manner, an elution amount of metal ions was found by the followingmethod.

The abutments to which the crown restorations were bonded were immersedin 80 mL of 1 wt % latic acid solution for three months. Thereafter, theelution amount of titanium in the solution was analyzed by a plasmaemission spectroscopy device.

3-2. Measurement of Fixing Strength

In respect of each of the dental implants of the examples and thecomparative examples to which the crown restorations were bonded in theabove manner (which dental implants were different from the dentalimplants used in Section 3-1 for measuring the elution amount of metalions), fixing strength (bonding strength) between the titanium memberand the ceramic member was found in the following method.

Using a jig as shown in FIG. 6, the abutment was attached to a fixingtable and a chuck was mounted to the male thread portion of theabutment. Then, the chuck was mounted to a tensile tester and a strengthtest was conducted by a drawing method.

3-3. Drop Test

In respect of each of the dental implants of the examples and thecomparative examples to which the crown restorations were bonded in theabove manner (which dental implants were different from the dentalimplants used in measuring the elution amount of metal ions in Section3-1 and the dental implants used in measuring the fixing strength inSection 3-2), a drop test was carried out in the following method.

The dental implants of the examples and the comparative examples towhich the crown restorations were bonded (ten dental implants of theexamples and ten dental implants of the comparative examples) weredropped one hundred times from a 2 m-high position onto a 2 cm-thickstainless steel plate.

External appearance of each of the dental implants thus dropped wasvisually observed and evaluated according to the following fourcriteria.

A: Cracks or defects were not recognized at all in the dental implants.

B: Tiny cracks or defects were recognized in one to five dentalimplants.

C: Noticeable cracks or defects were recognized in one to five dentalimplants, or tiny cracks or defects were recognized in six to ten dentalimplants.

D: Noticeable cracks or defects were recognized in six to ten dentalimplants.

Results of these evaluations were collectively shown in Table 3.

TABLE 3 Elution Amount of Fixing Metal Ions Strength [ppm] [MPa] DropTest Ex. 1 0.6 24 A Ex. 2 0.7 22 A Ex. 3 0.7 23 A Ex. 4 0.7 23 A Ex. 50.8 24 A Ex. 6 0.6 22 A Ex. 7 0.6 23 A Com. 12 — A Ex. 1 Com. 0 — D Ex.2 Com. 0.7 11 D Ex. 3

As is apparent in Table 3, the dental implants of the present inventionwere all sufficiently low in the elution amount of metal ions.Furthermore, in the dental implants of the present invention, the fixingstrength (joint strength) between the titanium members and the ceramicmembers was superior.

Moreover, the dental implants of the present invention exhibited nomismatching between themselves and the crown restorations, and nomismatching between the titanium members and the ceramic members.

In contrast, no satisfactory result was obtained in the comparativeexamples. More specifically, the elution amount of metal ions wasexceptionally high in Comparative Example 1 in which the abutment wascomposed of titanium alone.

Furthermore, the mechanical strength was low and the evaluation resultsof drop test were quite unsatisfactory in Comparative Example 2 in whichthe abutment was composed of ceramic (zirconia) alone. Moreover, in caseof Comparative Example 2, there was a problem in that the threadcoupling between the fixture and the abutment was highly likely to beloosened.

Additionally, in case of Comparative Example 3 in which the titaniummember and the ceramic member of the abutment were merely bonded by thedental cement, the bonding strength between the titanium member and theceramic member was not sufficiently great.

Therefore, the titanium member and the ceramic member were separatedfrom each other by a relatively weak force. Furthermore, in case ofComparative Example 3, the mechanical strength was low and theevaluation results of the drop test were quite unsatisfactory.

Further, in respect of Comparative Example 1, a quantity of the dentalcement used in bonding the dental implant (the abutment) and the crownrestoration was increased so that the dental implant and the crownrestoration should not make direct contact with each other.

Then, the same evaluation as noted above was conducted. The results ofthe evaluation revealed that the bonding strength between the dentalimplant and the crown restoration was sharply reduced (to 9 MPa).

Furthermore, if the quantity of dental cement was increased as mentionedabove, it became quite difficult, when bonding the crown restoration tothe abutment, to adjust a height and angle of the crown restorationfixed to the dental implant in conformity with the design.

What is claimed is:
 1. A dental implant including an abutment, wherein the abutment comprises a titanium member composed of a sintered body made from titanium or titanium alloy, and a ceramic member composed of a sintered body made from oxide-based ceramic; wherein the ceramic member has a recess and the titanium member has a protrusion inserted into the recess, wherein the protrusion has a heightwise axis and a cross-sectional area increasing portion whose cross-sectional area continuously increases from a base end of the protrusion to a dead-end portion of the recess, and the cross-sectional area increasing portion has a surface, wherein an angle between the surface of the cross-sectional area increasing portion and the heightwise axis of the protrusion is in a range of 0.3 to 5°, and wherein a cross-sectional shape of the protrusion is an elliptical shape, wherein the titanium member and the ceramic member are firmly fixed and joined together through an engagement between the protrusion and the recess, wherein said engagement is obtained due to the ceramic member with the recess contracting greater than the titanium member with the protrusion through a degreasing and sintering process, and wherein the protrusion conforms in shape to the recess.
 2. The dental implant as claimed in claim 1, wherein the ceramic member has a contact surface with which a metal member having a composition different from that of a constituent material of the titanium member is adapted to make contact, wherein the abutment is configured so that a crown having the metal member is fixed to the ceramic member, and the contact surface of the ceramic member is configured so as to prevent the metal member of the crown from being in contact with the titanium member.
 3. The dental implant as claimed in claim 2, wherein the contact surface is tapered toward an opposite direction with respect to the titanium member, and a maximum diameter of the ceramic member is larger than a maximum diameter of the titanium member.
 4. A dental implant including an abutment used to fix a crown to the abutment, wherein the abutment includes a ceramic member composed of a sintered body made from oxide-based ceramic, and having a recess and a contact surface provided opposite the recess, and a titanium member composed of a sintered body made from titanium or titanium alloy, and having a protrusion fitted to the recess, and wherein the crown includes a metal portion constituted of a metal composition different from a constituent material of the titanium member, and the metal portion is configured to be in contact with the contact surface, wherein the protrusion has a portion whose cross-sectional area continuously increases from a base end of the protrusion to a dead-end portion of the recess, wherein a cross-sectional shape of the protrusion is a non-circular shape an elliptical shape, wherein the titanium member and the ceramic member are firmly fixed and joined together through an engagement between the protrusion and the recess, wherein said engagement is obtained due to the ceramic member with the recess contracting greater than the titanium member with the protrusion through a degreasing and sintering process, and wherein after the crown is fixed to the ceramic member, the contact surface of the ceramic member is configured to prevent the metal portion of the crown from being in contact with the titanium member.
 5. The dental implant as claimed in claim 4, wherein the protrusion has a heightwise axis and the portion of the protrusion has a surface, wherein an angle between the surface of the portion and the heightwise axis of the protrusion is in a range of 0.3 to 5°.
 6. The dental implant as claimed in claim 4, wherein the contact surface is tapered toward an opposite direction with respect to the titanium member, and a maximum diameter of the ceramic member is larger than a maximum diameter of the titanium member. 